Skip dumping backtraces for cached processes

This change updates dumpstate to skip dumping backtraces for cached
processes. These processes are less likely to be causing
bugreport-necessitating issues, and if they are frozen, will cause
backtrace dumps to time out anyways.

This results in a ~50% decrease (21.327s -> 10.568s) in the time taken
to run DUMP TRACES.

Test: On a local device, check with bugreportz that there are no more
      timed-out backtrace dumps (i.e. that the "Dump failed, likely due
      to a timeout" failure no longer occurs).
Test: Run health/bugreport/capturebugreport on an internal build and
      verify that the DUMP TRACES section is much shorter.
Bug: 276451949
Change-Id: Iecb6c2168a0dccefecf3b92be24c647eaf729556

3 files changed, 28 insertions, 0 deletions

diff --git a/cmds/dumpstate/dumpstate.cpp b/cmds/dumpstate/dumpstate.cpp
index 7537237f65..bb4d58b153 100644
--- a/cmds/dumpstate/dumpstate.cpp
+++ b/cmds/dumpstate/dumpstate.cpp
@@ -2196,6 +2196,16 @@ Dumpstate::RunStatus Dumpstate::DumpTraces(const char** path) {
             continue;
         }
 
+        // Skip cached processes.
+        if (IsCached(pid)) {
+            // For consistency, the header and footer to this message match those
+            // dumped by debuggerd in the success case.
+            dprintf(fd, "\n---- pid %d at [unknown] ----\n", pid);
+            dprintf(fd, "Dump skipped for cached process.\n");
+            dprintf(fd, "---- end %d ----", pid);
+            continue;
+        }
+
         const std::string link_name = android::base::StringPrintf("/proc/%d/exe", pid);
         std::string exe;
         if (!android::base::Readlink(link_name, &exe)) {
diff --git a/libs/dumputils/dump_utils.cpp b/libs/dumputils/dump_utils.cpp
index 067ce17c33..97cb810404 100644
--- a/libs/dumputils/dump_utils.cpp
+++ b/libs/dumputils/dump_utils.cpp
@@ -16,6 +16,7 @@
 #include <set>
 
 #include <android-base/file.h>
+#include <android-base/parseint.h>
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
@@ -210,3 +211,18 @@ bool IsZygote(int pid) {
     return cmdline == "zygote" || cmdline == "zygote64" || cmdline == "usap32" ||
             cmdline == "usap64" || cmdline == "webview_zygote";
 }
+
+bool IsCached(int pid) {
+    std::string oom_score_adj;
+    if (!android::base::ReadFileToString(android::base::StringPrintf("/proc/%d/oom_score_adj",
+                                                                     pid),
+                                         &oom_score_adj)) {
+        return false;
+    }
+    int32_t oom_score_adj_value;
+    if (!android::base::ParseInt(android::base::Trim(oom_score_adj), &oom_score_adj_value)) {
+        return false;
+    }
+    // An OOM score greater than 900 indicates a cached process.
+    return oom_score_adj_value >= 900;
+}
diff --git a/libs/dumputils/include/dumputils/dump_utils.h b/libs/dumputils/include/dumputils/dump_utils.h
index 7c5329d01b..f973d9fb52 100644
--- a/libs/dumputils/include/dumputils/dump_utils.h
+++ b/libs/dumputils/include/dumputils/dump_utils.h
@@ -25,4 +25,6 @@ std::set<int> get_interesting_pids();
 
 bool IsZygote(int pid);
 
+bool IsCached(int pid);
+
 #endif  // DUMPUTILS_H_